1. Field of the Invention
This invention relates to a mass transfer apparatus which actively mixes a first mass with a second mass wherein the mass transfer apparatus has hollow fiber membranes carrying the first mass which are rotated or agitated within the second mass thus providing three-dimensional mass transfer. More particularly, this invention concerns a blood oxygenator comprising a rotor hub and a plurality of rotor members each having a plurality of hollow fiber membranes wherein the rotor hub supplies the hollow fiber membranes with oxygen and the plurality of rotor members rotate within the venous blood such that the oxygen which diffuses across the hollow fiber membranes is actively mixed with the venous blood flow.
2. Description of Related Art
The use of membrane oxygenators to oxygenate blood is well known in the art. One type of conventional membrane oxygenator employs bundles of hollow fibers retained within a cylindrical housing wherein oxygen is pumped through the hollow fibers in the same direction as the blood. The hollow fibers consist of a microporous membrane which is impermeable to blood and permeable to gas. Gas exchange takes place when venous blood flows through the housing and contacts the hollow fibers. Based on the law of diffusion the oxygen diffuses across the hollow fiber walls and enriches venous blood in contact with these hollow fibers. Examples of this type of membrane oxygenator are described in U.S. Pat. No. 4,620,965 issued to Fukusawa et al. and U.S. Pat. No. 4,698,207 issued to Bringham et al. The disadvantage to this type of membrane oxygenator is that a blood boundary layer is formed around the hollow fibers which retards oxygenation of blood that does not directly contact the hollow fibers.
Another type of conventional membrane oxygenator provides more efficient oxygenation of blood by positioning blood flow substantially perpendicular or at an angle to the hollow fiber membranes carrying the oxygen. Examples of this type of membrane oxygenator are described in U.S. Pat. No. 4,639,353 issued to Takemura et al., U.S. Pat. No. 3,998,593 issued to Yoshida et al. and U.S. Pat. No. 4,490,331 issued to Steg, Jr. A drawback to these designs is that the permeability of the hollow fiber membranes decreases over time and the oxygenator becomes less efficient.
Yet another type of membrane oxygenator discloses moving a part of the oxygenator in order to provide increased mixing of blood flow. Examples of this type of membrane oxygenator are described in U.S. Pat. Nos. 3,674,440 and 3,841,837 issued to Kitrilakis and Kitrilakis et al., respectively, (the Kitrilakis Patents) and U.S. Pat. No. 3,026,871 issued to Thomas (the Thomas Patent) The Kitrilakis Patents disclose a blood flow path and an oxygen flow path positioned between a rotor and a stator and separated by a membrane and a wafer. When the rotor rotates relative to the stator, mixing of blood flow occurs resulting in disruption of the blood boundary layer. Although this type of oxygenator provides a degree of mixing of blood, this type of mixing results in destruction of the red blood cells.
The Thomas Patent discloses rotating a cylindrical, semi-permeable membrane containing oxygen in a housing wherein blood contacts and flows over the membrane and oxygen is transferred through the rotating membrane to the blood. One disadvantage of this type of membrane oxygenator is that the permeability to oxygen and carbon dioxide of semipermeable membranes is poor.
Yet another type of blood oxygenator device comprises short microporous fiber sheets which are folded, twisted and woven around a hollow shaft that carries the inlet and outlet gas flows. The device is implanted into the vascular system of a patient and rotated to cause mixing of the blood. This type of device is explained in greater detail in xe2x80x9cA Dynamic Intravascular Lung,xe2x80x9d ASAIO Journal 1994. The problem with this type of blood oxygenator is that the number of fiber sheets that are able to be incorporated into the device is limited because the device is an intravascular device and therefore, anatomical space is is limited. Furthermore, the rotation of the device within the blood vessel may destroy the cells lining the blood vessel.
Nowhere in the cited related art is there disclosed or suggested a membrane oxygenator which provides effective blood oxygenation to sustain a patient for extended durations while also providing a compact oxygenator design. Therefore, there is a definite need for a blood membrane oxygenator incorporating an active mixing component which provides for effective blood oxygenation.
Accordingly, the present invention provides a blood oxygenator having a housing defining a blood path, a rotor hub defining an oxygen path, and at least one rotor defining a blood path and having a plurality of hollow fibers extending across the rotor blood path and being in fluid communication with the rotor hub oxygen path such that when oxygen flows through and diffuses across the plurality of hollow fibers and the rotor rotates about the rotor hub, active mixing of the blood occurs resulting in disruption of the blood boundary layer surrounding the hollow fibers.
Preferably, the rotor is a distributor disk having two oxygen return channels, two oxygen supply channels, a first spoke defining an oxygen inlet path, a second spoke defining an oxygen outlet path and a plurality of hollow fibers extending across the diameter of the disk and in fluid communication with the return and supply channels.
The present invention preferably provides a plurality of distributor disks positioned on the rotor hub thus, providing additional hollow fibers and increased surface area of the hollow fibers at which oxygenation of the blood takes place. The specific number of distributor disks is dependent upon the amount of surface area necessary for the specific patient. For example, a larger patient requires greater oxygen delivery and thus, more disks, however, fewer disks are necessary for a smaller patient. Further, the present invention provides for the surface area of the hollow fibers to be increased by increasing the number of hollow fibers on each distributor disk. Hollow fibers can extend from both the first and second faces of each of the distributor disk. By increasing or decreasing the number of distributor disks and hollow fibers used in the blood oxygenator of the present invention, the blood oxygenator capacity can be tailored to the specific patient application.
The present invention further provides for each of the plurality of rotors to be able to rotate independently of one another such that while some rotors rotate in the clockwise direction the other rotors simultaneously rotate in the counter-clockwise direction thus, providing an enhanced mixing of blood. Also, the plurality of rotors can be rotated in a back and forth motion such that the rotors repeatedly rotate approximately 360 degrees or less, and then reverse direction resulting in the blood being agitated and the blood boundary layer being disrupted.
Baffles are preferably positioned between the plurality of rotors in the blood oxygenator of the present invention in order to provide an increased mixing of the blood.
The rotor hub preferably takes the form of a double lumen shaft defining an oxygen inlet path and an oxygen outlet path.
The present invention provides for the plurality of hollow fibers to be microporous such that the fibers are impermeable to liquid and are permeable to gas. The present invention further provides for the opportunity of the surfaces of the hollow fibers to be coated with a material which would decrease the wetability of the microporous structure. An example of the type of material used for these purposes is silicone rubber, although numerous other polymer coatings could be used.
The present invention provides a blood oxygenator that can be used to treat patients having acute as well as chronic lung diseases.
Other details, objects and advantages of the present preferred invention will become more apparent with the following description of the present preferred invention.